Switching method for an electromagnetic switching device and an electromagnetic switching device corresponding thereto

ABSTRACT

The aim of the invention is to protect an electromagnetic switching device when a load ( 6 ) is switched to a supply voltage (U). A current (IL) that flows through the load contact ( 2 ) is monitored. The electric circuit is interrupted when the current (IL) exceeds a threshold value that is below the current carrying capacity of the load contact ( 2 ). The electric circuit is automatically closed again after the current (IL) which flows through the load contact ( 2 ) has decreased.

[0001] The present invention relates to a switching method for anelectromagnetic switching device, in particular a contactor, having atleast one load contact which has a current carrying capacity,

[0002] wherein the load contact is closed,

[0003] wherein the closing of the load contact closes a circuit,

[0004] wherein the circuit is opened when a current flowing through theload contact exceeds a current limit value,

[0005] and to an electromagnetic switching device which corresponds toit.

[0006] Switching methods and switching devices such as these are known.They are used, for example, in a series circuit comprising a contactorwith an upstream or downstream circuit breaker, or in the form of aso-called non-welding contactor. In both cases, the opening of thecircuit provides short-circuit protection for the contactor.

[0007] In some applications, an extremely high surge current flowsbriefly when the circuit is closed. In the case of transformers, thesurge current may amount to 20 to 30 times the continuous current, andin the case of capacitors it may even amount to 50 to 100 times thecontinuous current. The switching device must always be designed suchthat it can safely switch even this high surge current. The switchingdevice therefore has to be considerably overdesigned in order to switchtransformers or capacitors, in comparison to the continuous current tobe carried.

[0008] The object of the present invention is to specify a switchingmethod for an electromagnetic switching device and for theelectromagnetic switching device corresponding thereto, in which theswitching device may be designed to be smaller, without changing thecontinuous current which can be carried.

[0009] The object is achieved in that the circuit is closed againautomatically when the current flowing through the load contact fallsbelow the current limit value again as a result of the opening of thecircuit, and in that the current limit value is at most as great as thecurrent carrying capacity.

[0010] This is because, when the load is connected to the power supplysystem, the circuit is initially closed, and is then opened again beforethe current carrying capacity of the load contact is exceeded. The loadcontact is admittedly closed again immediately after this. The currentsurge which occurs when the load contact is closed for the second timeis, however, considerably less than the current surge which occurredpreviously. As a rule, this second current surge no longer exceeds thecurrent carrying capacity of the load contact. This thus means, forexample when connecting a capacitor, that it is possible to use aswitching device in which the current carrying capacity is, for example,25 times the continuous current to be carried instead of—as in the priorart—75 to 100—times the continuous current to be carried.

[0011] When the load contact is opened in order to open the circuit whenthe current limit value has been exceeded, no dedicated switch isrequired to open the circuit.

[0012] When the, current flows through an electromagnetic drive, whichis connected in series with the load contact, with the circuit closed,which electromagnetic drive opens a switching element, which isconnected in series with the electromagnetic drive, when the currentlimit value is exceeded, the circuit can be opened in a particularlysimple manner when the current limit value is exceeded.

[0013] If a pair of contact elements are electrically conductivelyconnected by a contact link to which a pressure spring applies apressure force in the direction of the pair of contact elements, inorder to close the load contact, and the electromagnetic drive actsdirectly on the contact link when the current limit value is exceededand lifts it off the pair of contact elements, the load currentmonitoring element responds particularly quickly.

[0014] If a deflection lever which is associated with theelectromagnetic drive is deflected from a rest position by a plunger,which is associated with the electromagnetic drive, when the currentlimit value is exceeded, and the deflection of the deflection leverlifts the contact link off the pair of contact elements, this results inthe electromagnetic switching device being particularly simple andcompact.

[0015] Further advantages and details can be found in the followingdescription of an exemplary embodiment. In this case, illustrated inoutline form, the single

[0016]FIG. 1 shows an electromagnetic switching device.

[0017] According to FIG. 1, a contactor as an example of anelectromagnetic switching device has a housing 1. A load contact 2 isarranged in the housing 1. The load contact 2 has a pair of contactelements 3 and a contact link 4. The pair of contact elements 3 areconnected firstly to a load voltage U and secondly via a load currentmonitoring element 5 to a load 6. The load 6 is in turn connected toground M.

[0018] In order to close the load contact 2, a switching current IS isapplied to a switching coil 7. In response, the switching coil 7 pullsin a main armature 8. The main armature 8 is connected to a contactsupport 9, which applies a pressure force via a pressure spring 10 tothe contact link 4, with this pressure force being in the direction ofthe pair of contact elements 3.

[0019] The attraction of the main armature 8 thus results in the pair ofcontact elements 3 being electrically conductively connected via thecontact link 4. The circuit is thus closed from the load voltage U viathe load 6 to ground M. In consequence, a load current IL flows via theload contact 2, the load current monitoring element 5 and the load 6.

[0020] The load current IL results in a contact opening force, which isdependent on the load current. The load current IL counteracts thepressure force. The pressure force thus defines a maximum current whichthe load current 2 can carry. This maximum current is the so-calledcurrent carrying capacity of the load contact 2.

[0021] Depending on the load 6, a very high inrush current surge canflow briefly when the load contact 2 is first closed. The inrush currentsurge may possibly exceed the current carrying capacity of the loadcontact 2. The load current monitoring element 5 is therefore providedin order to protect the load contact 2. This is connected in series withthe load contact 2, and is in the form of an electromagnetic drive. Ifthe load current IL exceeds a current limit value, which is at most asgreat as the current carrying capacity of the load contact 2, the loadcurrent monitoring element 5 trips. In consequence, it pulls in anauxiliary armature 11. In consequence, the contact link 4 of the loadcontact 2 is lifted off the pair of contacts 3 via a plunger 12 and adeflection lever 13. The circuit is thus likewise opened by opening ofthe load contact 2, to be precise by the electromagnetic drive actingdirectly on the contact link 4.

[0022] The opening of the load contact 2 also interrupts the currentflow through the load current monitoring element 5. It thus no longerexerts any pulling-in force on the auxiliary armature 11. The deflectionlever 13, the plunger 12 and the auxiliary armature 11 are thus movedback to a rest position once again, by means of a resetting spring 14.At the same time, the load contact 2 is closed again by the pressure ofthe pressure spring 10.

[0023] The entire abovementioned switching process takes place withoutany action on the drive side of the contactor. The switching coil 7 thusstill has the switching current IS applied to it despite the opening ofthe load contact 2, so that the main armature 8 and the contact support9 remain in the “contactor on” switch position.

[0024] In principle, the contactor described above can be used for allloads 6. However, its use is particularly advantageous if the load 6 isa transformer or a capacitor, since particularly high current surgesoccur in these two cases.

1. A switching method for an electromagnetic switching device, inparticular a contactor, having at least one load contact (2) which has acurrent carrying capacity, wherein the load contact (2) is closed,wherein the closing of the load contact (2) closes a circuit, whereinthe circuit is opened when a current (IL) flowing through the loadcontact (2) exceeds a current limit value, wherein the circuit is closedagain automatically when the current (IL) flowing through the loadcontact (2) falls below the current limit value again as a result of theopening of the circuit, and wherein the current limit value is at mostas great as the current carrying capacity.
 2. The switching method asclaimed in claim 1, characterized in that, when the current limit valueis exceeded, the load contact (2) is opened in order to open thecircuit.
 3. The switching method as claimed in claim 1 or 2,characterized in that, when the circuit is closed, the current (IL)flows through an electromagnetic drive (5), which is connected in serieswith the load contact (2) and which opens a switching element (2), whichis connected in series with the electromagnetic drive (5), when thecurrent limit value is exceeded.
 4. The switching method as claimed inclaims 2 and 3, characterized in that, in order to close the loadcontact (2), a pair of contact elements (3) are electricallyconductively connected by a contact link (4), to which a pressure forceis applied by a pressure spring (10) in the direction of the pair ofcontact elements (3), and in that the electromagnetic drive (5) actsdirectly on the contact link (4) when the current limit value isexceeded, and lifts it off the pair of contact elements (3).
 5. Theswitching method as claimed in claim 4, characterized in that adeflection lever (13), which is associated with the electromagneticdrive (5), is deflected from a rest position by a plunger (12) which isassociated with the electromagnetic drive (5), when the current limitvalue is exceeded, and in that the deflection of the deflection lever(13) lifts the contact link (4) off the pair of contact elements (3). 6.An electromagnetic switching device, in particular a contactor, havingat least one load contact (2), which has a current carrying capacity,and having a load current monitoring element (5), wherein a circuitwhich can be closed by the load contact (2) is opened by the loadcurrent monitoring element (5) when a current (IL) flowing through theload contact (2) exceeds a current limit value, wherein the circuit isautomatically closed again by the load current monitoring element (5)when the current (IL) flowing through the load contact (2) falls belowthe current limit value again as a result of the opening of the circuit,and wherein the load current monitoring element (5) is designed suchthat the current limit value is at most as great as the current carryingcapacity.
 7. The switching device as claimed in claim 6, characterizedin that the load current monitoring element (5) acts on the load contact(2).
 8. The switching device as claimed in claim 6 or 7, characterizedin that the load current monitoring element (5) is in the form of anelectromagnetic drive (5) which is connected in series with the loadcontact (2) and which opens a switching element (2), which is connectedin series with the electromagnetic drive (5), when the current limitvalue is exceeded.
 9. The switching device as claimed in claims 7 and 8,characterized in that the load contact (2) has a pair of contactelements (3) and a contact link (4), in that a pressure spring (10)applies a pressure force in the direction of the pair of contactelements (3) to the contact link (4), and in that the electromagneticdrive (5) acts directly on the contact link (4) when the current limitvalue is exceeded, and lifts it off the pair of contact elements (3).10. The switching device as claimed in claim 9, characterized in thatthe electromagnetic drive (5) has a plunger (12) and a deflection lever(13), in that the plunger (12) deflects the deflection lever (13) from arest position when the current limit value is exceeded, and in that thedeflection of the deflection lever (13) lifts the contact link (4) offthe pair of contact elements (3).